Liquid crystal material currently is used in a wide variety of devices, including, for example, optical devices such as visual displays. A property of liquid crystal enabling use in visual displays is the ability to scatter and/or to absorb light when the liquid crystal is in a random alignment and the ability to transmit light when the liquid crystal is in an ordered alignment.
Examples of electrically responsive liquid crystal material and use thereof are found in the above patent and applications and in U.S. Pat. No. 3,322,485. Certain types of liquid crystal material are responsive to a prescribed input, such as temperature or electrical input (electric field, voltage, frequency), changing the optical characteristics, such as the random or ordered alignment of the liquid crystal material, in response to temperature of the liquid crystal material or electric field voltage and/or frequency applied to the liquid crystal material.
Currently there are three categories of liquid crystal materials, namely cholesteric, nematic and smectic. The present invention preferably uses nematic liquid crystal material or a combination of nematic and some cholesteric type. More specifically, the liquid crystal material preferably is operationally nematic, i.e. it acts as nematic material and not as the other types. Operationally nematic means that in the absence of external fields structural distortion of the liquid crystal is dominated by the orientation of the liquid crystal at its boundaries rather than by bulk effects, such as very strong twists, as in cholesteric material, or layering, as in smectic material. Thus, for example, operationally nematic liquid crystal with chiral ingredients, which induce a tendency to twist but cannot overcome the effects of boundary alignment, still would be operationally nematic. Such material should have a positive dielectric anisotropy; as is described below, the liquid crystal may have both positive and negative dielectric anisotropy, e.g. as a function of frequency. The operationally nematic material may include nematic and cholesteric liquid crystal materials. Although various characteristics of the various liquid crystal materials are described in the prior art, one known characteristic is that of reversibility, e.g. of physical, structural, optical and/or electrical properties, as a prescribed input is applied or removed. Particularly, nematic liquid crystal material is known to be reversible, but cholesteric material ordinarily is not reversible.
Hereinbelow the liquid crystal of the invention primarily will be referred to interchangeably and equivalently as nematic or as operationally nematic.
Usually liquid crystal material is anisotropic both optically (birefringence) and, for example in the case of nematic material, electrically. The optical anisotropy is manifest by the absorption, especially when pleochroic dye is in solution with the liquid crystal material, of light when the liquid crystal material is in random alignment, and the transmission of light, especially in a particular direction related to an axis of the liquid crystal structure, through the liquid crystal material when it is in ordered alignment. The electrical anisotropy may be a relationship between the dielectric constant or dielectric coefficient with respect to the alignment of the liquid crystal material and also may be electrical frequency dependent.
Pleochroic dye also has been used in the past in a mixture with operationally nematic liquid crystal contained in plural volumes in a containment or support medium. Examples are given in several of the applicant's above-identified patent(s) and applications.
In the past, displays using liquid crystal material have had to be relatively small in size for a variety of reasons. Using applicant's invention of providing plural volumes of liquid crystal material in a support or containment medium, relatively large- and small-size displays can be made and operated successfully. The volumes may be discrete ones, may be interconnected with one or more other volumes, or may include both discrete and interconnected ones. Moreover, use of operationally nematic liquid crystal material enables operational response as a function of electrical input and also enables relatively expeditious and efficient operation, for example in response to the application or removal of an electric field.
As used herein with respect to the present invention, encapsulated liquid crystal material, volumes of liquid crystal material in a support or containment medium, etc., means liquid crystal material in capsules, cells or the like formed in or included in a containment medium. The capsules or cells may be discrete, i.e. not fluidically connected to any others, or may be fluidically interconnected with one or more capsules or cells. (The terms volumes, capsules, cells, etc. may be used interchangeably and equivalently herein.) Such liquid crystal material and containment medium may form an emulsion, preferably a stable one, that is able to set or to cure to a relatively stable structure in which the plural capsules, cells or volumes in the structure contain liquid crystal material and preferably also pleochroic dye. Various methods for making and using such encapsulated liquid crystal material and apparatus associated therewith are disclosed herein and in applicant's above patent(s) and applications.
In one preferred embodiment of the invention the containment medium is formed of a latex or latex type material, for example as is disclosed in copending U.S. patent application Ser. No. 591,433, filed Mar. 20, 1984, the entire disclosure of which is incorporated by reference. In another preferred embodiment the containment medium is polyvinyl alcohol.
A flat screen television system in which an electroluminescent array is repetitively scanned is disclosed in U.S. Pat. No. 3,627,924. Moreover, U.S. Pat. Nos. 3,636,244 and 3,639,685 disclose signal processing circuits for color television picture tubes. The disclosures of these patents are hereby incorporated by reference.